In many applications such as airborne units, it is necessary for compressors to operate at different attitudes, i.e., vertically, horizontally or even upside down in relation to the prevailing gravity field. The flexibility of the compressor in these applications is usually limited by the operation of the associated lubrication system which requires an oil reservoir designed appropriately to provide a continuous supply of lubricant to the compressor bearings. When the supply of lubricant is interrupted as by flight maneuvers, it is important that it be restarted very rapidly in order to avoid mechanical damage.
One approach of the prior art has been to hermetically encapsulate the compressor, using a horizontally disposed hollow crank shaft of the type that is disclosed in U.S. Pat. No. 4,729,728. The source of power for oil pumping in this case is derived from a jet pump energized by a gaseous discharge stream from the compressor which is caused to expand in a jet nozzle thereby creating a suction which draws oil up through a suction tube and pumps the mixture through the hollow shaft. With this arrangement, centrifugal forces due to shaft rotation will provide some degree of separation such that the oil will move radially outward to feed the bearings and the gas will be discharged into the canister around the compressor housing.
Unfortunately, the arrangement disclosed in U.S. Pat. No. 4,729,728 will work best near the design operating point. On the other hand, it will be mismatched at other points and during start-up. Additionally, it will also back pressure the compressor under such conditions.
Still further, U.S. Pat. No. 4,729,728 teaches the use of a swiveling and rotatable suction tube. This tube is inherently designed to move in accordance with gravitational forces so as to follow the movement of oil in the reservoir. While of interest, this would not be suitable for airborne applications wherein weight is a factor.
Specifically, the swiveling and rotatable suction tube must, by definition, be designed in a manner to cause a weight penalty. This follows from the fact that a very light suction tube may well not be able to overcome frictional forces at the pivot point. For this reason, it has remained to provide an entirely satisfactory oil supply system for a compressor capable of operation at different attitudes.
The present invention is directed to overcoming one or more of the foregoing problems and achieving one or more of the resulting objects.